Transforming Spent Railroad Ties into High-Value Biochar: A Sustainable Solution for Phosphorus and Nitrate Removal in Water Treatment

The growing challenge of managing end-of-life creosote-treated railroad ties, along with the increasing demand for effective water treatment solutions, has highlighted the potential of converting railroad tie biomass into functional biochar through pyrolysis. Pyrolysis temperatures ranging from 250 °C to 700 °C were evaluated to determine their influence on biochar yield, physicochemical properties, and adsorption performance for nitrate and phosphate. The findings revealed that increasing pyrolysis temperature enhanced biochar surface area and porosity, reaching 454.9 m2/g at 700 °C. Elemental analyses showed maximum carbonization at 550 °C, with carbon content peaking at 80%, reflecting the development of more stable aromatic structures. SEM and FTIR analyses confirmed these structural changes, including the emergence of extensive pore networks and aromatic frameworks. Biochar produced at 600 °C demonstrated high nitrate (80%) and phosphate (79%) removal efficiencies, following Freundlich isotherm models. Magnesium-modified biochar further improved nitrate adsorption, reaching 90% removal at 5 ppm. Importantly, polycyclic aromatic hydrocarbons in the biochar decreased significantly at higher temperatures, ensuring environmental safety. This work demonstrates the dual environmental benefits of converting hazardous railroad tie waste into value-added biochar for nutrient removal in water treatment applications, offering a sustainable and scalable solution for circular waste management.